How to Install Classic Instruments in a Vintage Panel

Jump in any modern car and get set to fire it up and chances are the dashboard will light up like a pinball machine gone berserk. Warning lights (also referred to as telltale lights by many manufacturers, and idiot lights by most automotive enthusiasts) will indicate a variety of malfunctions, including pressures and temperatures that are outside of the normal range, emission system failures, doors that aren't closed, low fuel levels, and there's probably one that glows brightly when the current payment is late.

Indicator lights in place of gauges aren't really new; Hudson used them to indicate low oil pressure and low generator output in the 1930s. The argument then as now is that drivers don't pay much attention to the gauges, so consequently a warning light is more likely to get noticed. But while that may apply to the average motorist, those who look at their cars as more than a means of transportation like to keep tabs on their vehicle's vital functions, and the best way to do that is with an accurate instrument.

2/13Matt’s 1956 Ford was originally equipped with a padded dash that was secured by chrome. The pad was removed earlier and the dash repainted. When the gauges were replaced the trim was tossed and the screw holes filled.

Over the past year or so teenager Matt Love has been giving his first car, a 1956 Ford, the street rod treatment. Under the watchful eye of his proud pop, longtime street rodder and Vintage Air VP Rick Love, the Vicky hardtop has received a number of updates, and now it was time to enhance the instrumentation.

In stock form the Ford featured a speedometer, fuel level and temperature gauges, warning lights for low oil pressure and generator output, and a clock. Presumably the timepiece was there so the driver would know how long the car ran after one or more idiot lights came on.

3/13The original dash panel was removed with the gauges in place and then it was off to Classic Instruments for a do over. As the stock gauges were an unusual size, a new instrument panel was fabricated.

To update the Ford's dash panel Matt turned to John McLeod at Classic Instruments. Classic not only offers a complete assortment of gauges in a wide variety of configurations but they design and build custom instruments and do retrofits. As the term "custom" implies, Classic Instruments has created one-off gauges for a long list of the finest cars built by the most notable builders. The retrofit process, as Mcleod describes it, is not a restoration of instrumentation but rather the fitting of gauges in stock locations using the original housing. "You can keep the look of your gauges nearly original in appearance or customize them to fit your project." Matt chose gauges that were close to original in appearance but far better in terms of accuracy.

Automotive gauges can be divided into two basic categories, mechanical and electric. At one time mechanical gauges were favored because "those are what race cars have". Of course most early race cars didn't have an electrical system so that narrowed the options. In fact, the best reason for using mechanical gauges was that they had greater indicator needle range—the numbers could be spread out, making them easier to read than the typical short-sweep electrical gauges. But, thanks to modern technology, that has changed. With the development of the air core movements and sophisticated circuitry, electric gauges can have up to 300 degrees of pointer movement, as much as will be found on most mechanical gauges, with unparalleled accuracy.

4/13Classic Instrument’s in-house design staff has created unique instrument panel designs for the best builders in the country, countless show winners and many, many satisfied customers. This is the proposal for Matt’s 1956 Ford.

In most cases, when retrofitting an older instrument panel the range of the oil pressure and temperature gauges will be increased, a voltmeter will be substituted for an ammeter, and the speedometer will be electric rather than mechanical.

5/13It may look like a bundle of wires, but this is a modern air core movement for an electric gauge. Accurate and reliable, the internal damping of the movement results in steady readings from stable pointers.

Speedometer
Classic Instruments 3-3/8- and 4-5/8-inch electric speedometers read an electrical signal ranging from 11,000 to 110,000 pulses per mile. Speedometers are calibrated by resetting the "DIP" switches after a road test. The odometer counter then re-synchronizes to the new, corrected pointer reading.

Signals for electronic speedometers can be generated a variety of ways:

6/13To accommodate the replacement gauges and indicator lights a new instrument panel was fabricated. It was painted to match the stock dash.

SN16 pulse signal generator: used on GM or Chrysler transmissions that have a mechanical speedometer cable drive. The pulse signal generator replaces the speedometer cable and produces a "square wave", which alternates between 0 and +12 V. The SN16 is a powered signal generator, which means it requires +12 V to operate, unlike some two-wire pulse signal generators that create their own voltage.

SN17 Ford pulse signal generator adapter: used to convert the connection from Ford and similar transmissions that have a mechanical speedometer drive cable to work with the SN16.

SN74 speedometer signal interface: used to convert speed signals from electronic transmissions or vehicle computers to one that is compatible with the Classic Instruments speedometer. Calibration couldn't be easier than simply a matter of pushing a button. Some Classic Instruments speedometers have the SN74 functionality built into them with no signal interface needed.

SN81 GPS speedometer signal: Called the Sky Drive, it uses GPS satellite signals to operate an electronic speedometer. It updates 10 times per second and eliminates the need for ECU convertors or pulse signal generators screwed onto the transmission.
SN78SM magnetic proximity speed sensor: This sensor has a magnetic head, which senses targets attached to the drive shaft or brake rotor. The SN78SM will provide a +12V pulse upon detection of each target.

7/13Included with the gauges is a harness with color-coded wires and quick-disconnect plugs. The harness also comes with corresponding plugs to be added to the car’s wiring harness. Note the DIP switches at the top of the speedometer (center gauge) used for calibration.

Fuel Gauge
The most common Classic Instruments fuel level sender has a resistance range of 240 ohms empty and 33 ohms on full. Other senders available operate in resistance ranges of:

~0 to ~30 ohms (typically used with original GM fuel gauges before 1964)

~0 to ~90 ohms (typically used with original GM fuel gauges after 166)

~78 to ~10 ohms (typically used with original Ford fuel gauges before 1986)

Classic Instruments offers fuel gauges that work with these senders and more (check with them for gauge/sender compatibility).

8/13Here the new panel has been attached to the stock “eyebrow” and is ready to be slipped back in place. The notch at the bottom is for the gear position indicator.

We should add that a good ground at the sender is necessary for the fuel level gauge to operate properly. Don't rely on the tank to provide the ground, as most are electrically isolated—run a dedicated ground wire from the sender to the chassis. A bad or missing ground will make gauges with 240-33 and 75-10 operating ranges to peg below empty—0-30, 0-90, and 16-158 fuel gauges will peg above full.

Oil Pressure Gauge
Classic Instruments oil pressure gauges require the proper sender for the range of the instrument (0 to 80, or 0 to 100 psi). The lower the resistance, the higher the reading on the gauge. Because of this, the sender must be properly grounded to provide the proper signal or the gauge will read low or peg below 0 psi. Pipe sealer should be used sparingly on the threads of the sender and Teflon tape should not be used.

Temperature Gauge
Temperature senders should be mounted in the intake manifold of the engine when possible. Installing the sender in the head or in close proximity to other heat sources (i.e. exhaust headers) will cause the temperature gauge to read high. Additionally, bushings should not be used to make a temperature sender fit as they can cause the sender probe to not be fully submerged in the coolant (this could cause the sender to measure coolant vapor temperature, which is usually higher than the actual coolant temperature). All Classic Instruments temperature gauges require the correct sender—they are available to fit most stock or aftermarket intake manifolds.

9/13Fords of this era had a very simple electrical system that used inline fuses rather than a fuse block. Matt and Rick added a small fuse panel to power the gauges and other accessories.

Volt Gauge
The volt gauge does not require a signal like the temperature, oil pressure, and fuel level gauges do. The volt gauge is simply connected to a good ground and switched battery power.

Tachometer
Although Matt did not opt for a tachometer, when one is used it can get a signal from a computer, ignition module, or coil. Some signals require an adapter to work correctly.

10/13Included with the gauges was a new oil pressure sender. Sealant approved for use on electrical senders was used rather than Teflon tape—sealant allow the sender to have a good ground, Teflon tape doesn’t.

Installation
The new instruments made it necessary to install the proper oil pressure and temperature senders, however the original fuel tank sender was retained, as it was compatible with the replacement gas gauge. An electrical source for the voltmeter was needed, an adapter cable for the speedometer's pulse generator was necessary and then it was simply a matter of reinstalling the dash panel.

With the gauges in place and the new senders installed Matt's 1956 has a real dash of class with a vintage look he was after along with the reliability and accuracy of state-of-the-art gauges. And there are no idiot lights to tell him too little too late.